Managing event count reports in a tile-based architecture

ABSTRACT

One embodiment of the present invention sets forth a graphics processing system configured to track event counts in a tile-based architecture. The graphics processing system includes a screen-space pipeline and a tiling unit. The screen-space pipeline includes a first unit, a count memory associated with the first unit, and an accumulating memory associated with the first unit. The first unit is configured to detect an event type and increment the count memory. The tiling unit is configured to cause the screen-space pipeline to update an external memory address to reflect a first value stored in the count memory when the first unit completes processing of a first set of primitives. The tiling unit is also configured to cause the screen-space pipeline to update the accumulating memory to reflect a second value stored in the count memory when the first unit completes processing of a second set of primitives.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. non-provisional patentapplication Ser. No. 14/046,249, filed Oct. 4, 2013 and titled “MANAGINGEVENT COUNT REPORTS IN A TILE-BASED ARCHITECTURE”, which claims benefitof U.S. provisional patent application Ser. No. 61/719,271, filed Oct.26, 2012 and titled “AN APPROACH FOR TILED CACHING.” The subject matterof these related applications is hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention relate generally to graphicsprocessing and, more specifically, to managing event count reports in atile-based architecture.

Description of the Related Art

In typical operation, a graphics processing pipeline may be directed toprovide a count of a number of occurrences of a certain event. Forexample, the graphics processing pipeline may be directed to record thenumber of pixels that pass a z-test or the number of pixels for which aspecified operation is performed in the pixel shader. Such counts may beuseful to an application, which may condition certain work on suchcounts. For example, certain rendering operations may be conditioned onthe count associated with a “z-pass pixel test,” where those renderingoperations are performed only when the number of pixels that pass az-test exceeds a certain threshold value.

Some graphics subsystems for rendering graphics images implement atiling architecture, where one or more render targets, such as a framebuffer, are divided into screen space partitions referred to as “tiles.”In such a tiling architecture, the graphics subsystem rearranges worksuch that the work associated with any particular tile remains in anon-chip cache for a longer time than with an architecture that does notrearrange work in this manner. This rearrangement helps to improvememory bandwidth as compared with a non-tiling architecture.

In graphics subsystems that implement a tiling architecture and re-orderwork, the event counts discussed above may not provide the desiredresults. More specifically, because the work is re-ordered, themechanisms that record the requested counts may record incorrectnumbers. For example, a first set of work and a second set of work couldbe divided into several subsets, each associated with a different tile,which would then be interleaved. If a count request were to request anevent count associated with the first set of work, then when the firstset of work and second set of work were interleaved, the count requestwould include values associated with both the first set of work and thesecond set of work, which is not what is requested.

As the foregoing illustrates, what is needed in the art is a moreeffective technique for counting event occurrences in a tile-basedarchitecture.

SUMMARY OF THE PRESENT INVENTION

One embodiment of the present invention sets forth a graphics processingsystem configured to track event counts in a tile-based architecture.The graphics processing system includes a screen-space pipeline and atiling unit. The screen-space pipeline includes a first unit, a countmemory associated with the first unit, and an accumulating memoryassociated with the first unit. The first unit is configured to detectan event type and increment the count memory in response. The tilingunit is configured to cause the screen-space pipeline to update anexternal memory address to reflect a first value stored in the countmemory when the first unit completes processing of a first set ofprimitives that overlap a first cache tile. The tiling unit is alsoconfigured to cause the screen-space pipeline to update the accumulatingmemory to reflect a second value stored in the count memory when thefirst unit completes processing of a second set of primitives thatoverlap the first cache tile. At least one primitive in the first set ofprimitives and at least one primitive in the second set of primitivesare configured to cause the first unit to detect the event type andincrement the count memory.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a block diagram illustrating a computer system configured toimplement one or more aspects of the present invention;

FIG. 2 is a block diagram of a parallel processing unit included in theparallel processing subsystem of FIG. 1, according to one embodiment ofthe present invention;

FIG. 3A is a block diagram of a general processing cluster included inthe parallel processing unit of FIG. 2, according to one embodiment ofthe present invention;

FIG. 3B is a conceptual diagram of a graphics processing pipeline thatmay be implemented within the parallel processing unit of FIG. 2,according to one embodiment of the present invention;

FIG. 4 is a conceptual diagram of a cache tile that the graphicsprocessing pipeline of FIG. 3B may be configured to generate andprocess, according to one embodiment of the present invention;

FIG. 5 is a block diagram of a graphics subsystem configured toimplement cache tiling, according to one embodiment of the presentinvention;

FIG. 6 is a workflow diagram conceptually illustrating cache tilebatches produced by a tiling unit, according to one embodiment of thepresent invention;

FIG. 7 conceptually illustrates a sequence of operations associated withthe tiling unit, for managing event counts, according to one embodimentof the present invention;

FIG. 8 is a workflow diagram conceptually illustrating work associatedwith cache tile batches produced by a tiling unit for a single flushoperation, according to one embodiment of the present invention;

FIG. 9 is a workflow diagram conceptually illustrating work associatedwith cache tile batches produced by a tiling unit for two flushoperations, according to one embodiment of the present invention; and

FIG. 10 is a flow diagram of method steps for recording event counts ina tile-based architecture, according to one embodiment of the presentinvention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the present invention. However,it will be apparent to one of skill in the art that the presentinvention may be practiced without one or more of these specificdetails.

System Overview

FIG. 1 is a block diagram illustrating a computer system 100 configuredto implement one or more aspects of the present invention. As shown,computer system 100 includes, without limitation, a central processingunit (CPU) 102 and a system memory 104 coupled to a parallel processingsubsystem 112 via a memory bridge 105 and a communication path 113.Memory bridge 105 is further coupled to an I/O (input/output) bridge 107via a communication path 106, and I/O bridge 107 is, in turn, coupled toa switch 116.

In operation, I/O bridge 107 is configured to receive user inputinformation from input devices 108, such as a keyboard or a mouse, andforward the input information to CPU 102 for processing viacommunication path 106 and memory bridge 105. Switch 116 is configuredto provide connections between I/O bridge 107 and other components ofthe computer system 100, such as a network adapter 118 and variousadd-in cards 120 and 121.

As also shown, I/O bridge 107 is coupled to a system disk 114 that maybe configured to store content and applications and data for use by CPU102 and parallel processing subsystem 112. As a general matter, systemdisk 114 provides non-volatile storage for applications and data and mayinclude fixed or removable hard disk drives, flash memory devices, andCD-ROM (compact disc read-only-memory), DVD-ROM (digital versatiledisc-ROM), Blu-ray, HD-DVD (high definition DVD), or other magnetic,optical, or solid state storage devices. Finally, although notexplicitly shown, other components, such as universal serial bus orother port connections, compact disc drives, digital versatile discdrives, film recording devices, and the like, may be connected to I/Obridge 107 as well.

In various embodiments, memory bridge 105 may be a Northbridge chip, andI/O bridge 107 may be a Southbrige chip. In addition, communicationpaths 106 and 113, as well as other communication paths within computersystem 100, may be implemented using any technically suitable protocols,including, without limitation, AGP (Accelerated Graphics Port),HyperTransport, or any other bus or point-to-point communicationprotocol known in the art.

In some embodiments, parallel processing subsystem 112 comprises agraphics subsystem that delivers pixels to a display device 110 that maybe any conventional cathode ray tube, liquid crystal display,light-emitting diode display, or the like. In such embodiments, theparallel processing subsystem 112 incorporates circuitry optimized forgraphics and video processing, including, for example, video outputcircuitry. As described in greater detail below in FIG. 2, suchcircuitry may be incorporated across one or more parallel processingunits (PPUs) included within parallel processing subsystem 112. In otherembodiments, the parallel processing subsystem 112 incorporatescircuitry optimized for general purpose and/or compute processing.Again, such circuitry may be incorporated across one or more PPUsincluded within parallel processing subsystem 112 that are configured toperform such general purpose and/or compute operations. In yet otherembodiments, the one or more PPUs included within parallel processingsubsystem 112 may be configured to perform graphics processing, generalpurpose processing, and compute processing operations. System memory 104includes at least one device driver 103 configured to manage theprocessing operations of the one or more PPUs within parallel processingsubsystem 112.

In various embodiments, parallel processing subsystem 112 may beintegrated with one or more other the other elements of FIG. 1 to form asingle system. For example, parallel processing subsystem 112 may beintegrated with CPU 102 and other connection circuitry on a single chipto form a system on chip (SoC).

It will be appreciated that the system shown herein is illustrative andthat variations and modifications are possible. The connection topology,including the number and arrangement of bridges, the number of CPUs 102,and the number of parallel processing subsystems 112, may be modified asdesired. For example, in some embodiments, system memory 104 could beconnected to CPU 102 directly rather than through memory bridge 105, andother devices would communicate with system memory 104 via memory bridge105 and CPU 102. In other alternative topologies, parallel processingsubsystem 112 may be connected to I/O bridge 107 or directly to CPU 102,rather than to memory bridge 105. In still other embodiments, I/O bridge107 and memory bridge 105 may be integrated into a single chip insteadof existing as one or more discrete devices. Lastly, in certainembodiments, one or more components shown in FIG. 1 may not be present.For example, switch 116 could be eliminated, and network adapter 118 andadd-in cards 120, 121 would connect directly to I/O bridge 107.

FIG. 2 is a block diagram of a parallel processing unit (PPU) 202included in the parallel processing subsystem 112 of FIG. 1, accordingto one embodiment of the present invention. Although FIG. 2 depicts onePPU 202, as indicated above, parallel processing subsystem 112 mayinclude any number of PPUs 202. As shown, PPU 202 is coupled to a localparallel processing (PP) memory 204. PPU 202 and PP memory 204 may beimplemented using one or more integrated circuit devices, such asprogrammable processors, application specific integrated circuits(ASICs), or memory devices, or in any other technically feasiblefashion.

In some embodiments, PPU 202 comprises a graphics processing unit (GPU)that may be configured to implement a graphics rendering pipeline toperform various operations related to generating pixel data based ongraphics data supplied by CPU 102 and/or system memory 104. Whenprocessing graphics data, PP memory 204 can be used as graphics memorythat stores one or more conventional frame buffers and, if needed, oneor more other render targets as well. Among other things, PP memory 204may be used to store and update pixel data and deliver final pixel dataor display frames to display device 110 for display. In someembodiments, PPU 202 also may be configured for general-purposeprocessing and compute operations.

In operation, CPU 102 is the master processor of computer system 100,controlling and coordinating operations of other system components. Inparticular, CPU 102 issues commands that control the operation of PPU202. In some embodiments, CPU 102 writes a stream of commands for PPU202 to a data structure (not explicitly shown in either FIG. 1 or FIG.2) that may be located in system memory 104, PP memory 204, or anotherstorage location accessible to both CPU 102 and PPU 202. A pointer tothe data structure is written to a pushbuffer to initiate processing ofthe stream of commands in the data structure. The PPU 202 reads commandstreams from the pushbuffer and then executes commands asynchronouslyrelative to the operation of CPU 102. In embodiments where multiplepushbuffers are generated, execution priorities may be specified foreach pushbuffer by an application program via device driver 103 tocontrol scheduling of the different pushbuffers.

As also shown, PPU 202 includes an I/O (input/output) unit 205 thatcommunicates with the rest of computer system 100 via the communicationpath 113 and memory bridge 105. I/O unit 205 generates packets (or othersignals) for transmission on communication path 113 and also receivesall incoming packets (or other signals) from communication path 113,directing the incoming packets to appropriate components of PPU 202. Forexample, commands related to processing tasks may be directed to a hostinterface 206, while commands related to memory operations (e.g.,reading from or writing to PP memory 204) may be directed to a crossbarunit 210. Host interface 206 reads each pushbuffer and transmits thecommand stream stored in the pushbuffer to a front end 212.

As mentioned above in conjunction with FIG. 1, the connection of PPU 202to the rest of computer system 100 may be varied. In some embodiments,parallel processing subsystem 112, which includes at least one PPU 202,is implemented as an add-in card that can be inserted into an expansionslot of computer system 100. In other embodiments, PPU 202 can beintegrated on a single chip with a bus bridge, such as memory bridge 105or I/O bridge 107. Again, in still other embodiments, some or all of theelements of PPU 202 may be included along with CPU 102 in a singleintegrated circuit or system of chip (SoC).

In operation, front end 212 transmits processing tasks received fromhost interface 206 to a work distribution unit (not shown) withintask/work unit 207. The work distribution unit receives pointers toprocessing tasks that are encoded as task metadata (TMD) and stored inmemory. The pointers to TMDs are included in a command stream that isstored as a pushbuffer and received by the front end unit 212 from thehost interface 206. Processing tasks that may be encoded as TMDs includeindices associated with the data to be processed as well as stateparameters and commands that define how the data is to be processed. Forexample, the state parameters and commands could define the program tobe executed on the data. The task/work unit 207 receives tasks from thefront end 212 and ensures that GPCs 208 are configured to a valid statebefore the processing task specified by each one of the TMDs isinitiated. A priority may be specified for each TMD that is used toschedule the execution of the processing task. Processing tasks also maybe received from the processing cluster array 230. Optionally, the TMDmay include a parameter that controls whether the TMD is added to thehead or the tail of a list of processing tasks (or to a list of pointersto the processing tasks), thereby providing another level of controlover execution priority.

PPU 202 advantageously implements a highly parallel processingarchitecture based on a processing cluster array 230 that includes a setof C general processing clusters (GPCs) 208, where C≧1. Each GPC 208 iscapable of executing a large number (e.g., hundreds or thousands) ofthreads concurrently, where each thread is an instance of a program. Invarious applications, different GPCs 208 may be allocated for processingdifferent types of programs or for performing different types ofcomputations. The allocation of GPCs 208 may vary depending on theworkload arising for each type of program or computation.

Memory interface 214 includes a set of D of partition units 215, whereD≧1. Each partition unit 215 is coupled to one or more dynamic randomaccess memories (DRAMs) 220 residing within PPM memory 204. In oneembodiment, the number of partition units 215 equals the number of DRAMs220, and each partition unit 215 is coupled to a different DRAM 220. Inother embodiments, the number of partition units 215 may be differentthan the number of DRAMs 220. Persons of ordinary skill in the art willappreciate that a DRAM 220 may be replaced with any other technicallysuitable storage device. In operation, various render targets, such astexture maps and frame buffers, may be stored across DRAMs 220, allowingpartition units 215 to write portions of each render target in parallelto efficiently use the available bandwidth of PP memory 204.

A given GPCs 208 may process data to be written to any of the DRAMs 220within PP memory 204. Crossbar unit 210 is configured to route theoutput of each GPC 208 to the input of any partition unit 215 or to anyother GPC 208 for further processing. GPCs 208 communicate with memoryinterface 214 via crossbar unit 210 to read from or write to variousDRAMs 220. In one embodiment, crossbar unit 210 has a connection to I/Ounit 205, in addition to a connection to PP memory 204 via memoryinterface 214, thereby enabling the processing cores within thedifferent GPCs 208 to communicate with system memory 104 or other memorynot local to PPU 202. In the embodiment of FIG. 2, crossbar unit 210 isdirectly connected with I/O unit 205. In various embodiments, crossbarunit 210 may use virtual channels to separate traffic streams betweenthe GPCs 208 and partition units 215.

Again, GPCs 208 can be programmed to execute processing tasks relatingto a wide variety of applications, including, without limitation, linearand nonlinear data transforms, filtering of video and/or audio data,modeling operations (e.g., applying laws of physics to determineposition, velocity and other attributes of objects), image renderingoperations (e.g., tessellation shader, vertex shader, geometry shader,and/or pixel/fragment shader programs), general compute operations, etc.In operation, PPU 202 is configured to transfer data from system memory104 and/or PP memory 204 to one or more on-chip memory units, processthe data, and write result data back to system memory 104 and/or PPmemory 204. The result data may then be accessed by other systemcomponents, including CPU 102, another PPU 202 within parallelprocessing subsystem 112, or another parallel processing subsystem 112within computer system 100.

As noted above, any number of PPUs 202 may be included in a parallelprocessing subsystem 112. For example, multiple PPUs 202 may be providedon a single add-in card, or multiple add-in cards may be connected tocommunication path 113, or one or more of PPUs 202 may be integratedinto a bridge chip. PPUs 202 in a multi-PPU system may be identical toor different from one another. For example, different PPUs 202 mighthave different numbers of processing cores and/or different amounts ofPP memory 204. In implementations where multiple PPUs 202 are present,those PPUs may be operated in parallel to process data at a higherthroughput than is possible with a single PPU 202. Systems incorporatingone or more PPUs 202 may be implemented in a variety of configurationsand form factors, including, without limitation, desktops, laptops,handheld personal computers or other handheld devices, servers,workstations, game consoles, embedded systems, and the like.

FIG. 3A is a block diagram of a GPC 208 included in PPU 202 of FIG. 2,according to one embodiment of the present invention. In operation, GPC208 may be configured to execute a large number of threads in parallelto perform graphics, general processing and/or compute operations. Asused herein, a “thread” refers to an instance of a particular programexecuting on a particular set of input data. In some embodiments,single-instruction, multiple-data (SIMD) instruction issue techniquesare used to support parallel execution of a large number of threadswithout providing multiple independent instruction units. In otherembodiments, single-instruction, multiple-thread (SIMT) techniques areused to support parallel execution of a large number of generallysynchronized threads, using a common instruction unit configured toissue instructions to a set of processing engines within GPC 208. Unlikea SIMD execution regime, where all processing engines typically executeidentical instructions, SIMT execution allows different threads to morereadily follow divergent execution paths through a given program.Persons of ordinary skill in the art will understand that a SIMDprocessing regime represents a functional subset of a SIMT processingregime.

Operation of GPC 208 is controlled via a pipeline manager 305 thatdistributes processing tasks received from a work distribution unit (notshown) within task/work unit 207 to one or more streamingmultiprocessors (SMs) 310. Pipeline manager 305 may also be configuredto control a work distribution crossbar 330 by specifying destinationsfor processed data output by SMs 310.

In one embodiment, GPC 208 includes a set of M of SMs 310, where M≧1.Also, each SM 310 includes a set of functional execution units (notshown), such as execution units and load-store units. Processingoperations specific to any of the functional execution units may bepipelined, which enables a new instruction to be issued for executionbefore a previous instruction has completed execution. Any combinationof functional execution units within a given SM 310 may be provided. Invarious embodiments, the functional execution units may be configured tosupport a variety of different operations including integer and floatingpoint arithmetic (e.g., addition and multiplication), comparisonoperations, Boolean operations (AND, OR, XOR), bit-shifting, andcomputation of various algebraic functions (e.g., planar interpolationand trigonometric, exponential, and logarithmic functions, etc.).Advantageously, the same functional execution unit can be configured toperform different operations.

In operation, each SM 310 is configured to process one or more threadgroups. As used herein, a “thread group” or “warp” refers to a group ofthreads concurrently executing the same program on different input data,with one thread of the group being assigned to a different executionunit within an SM 310. A thread group may include fewer threads than thenumber of execution units within the SM 310, in which case some of theexecution may be idle during cycles when that thread group is beingprocessed. A thread group may also include more threads than the numberof execution units within the SM 310, in which case processing may occurover consecutive clock cycles. Since each SM 310 can support up to Gthread groups concurrently, it follows that up to G*M thread groups canbe executing in GPC 208 at any given time.

Additionally, a plurality of related thread groups may be active (indifferent phases of execution) at the same time within an SM 310. Thiscollection of thread groups is referred to herein as a “cooperativethread array” (“CTA”) or “thread array.” The size of a particular CTA isequal to m*k, where k is the number of concurrently executing threads ina thread group, which is typically an integer multiple of the number ofexecution units within the SM 310, and m is the number of thread groupssimultaneously active within the SM 310.

Although not shown in FIG. 3A, each SM 310 contains a level one (L1)cache or uses space in a corresponding L1 cache outside of the SM 310 tosupport, among other things, load and store operations performed by theexecution units. Each SM 310 also has access to level two (L2) caches(not shown) that are shared among all GPCs 208 in PPU 202. The L2 cachesmay be used to transfer data between threads. Finally, SMs 310 also haveaccess to off-chip “global” memory, which may include PP memory 204and/or system memory 104. It is to be understood that any memoryexternal to PPU 202 may be used as global memory. Additionally, as shownin FIG. 3A, a level one-point-five (L1.5) cache 335 may be includedwithin GPC 208 and configured to receive and hold data requested frommemory via memory interface 214 by SM 310. Such data may include,without limitation, instructions, uniform data, and constant data. Inembodiments having multiple SMs 310 within GPC 208, the SMs 310 maybeneficially share common instructions and data cached in L1.5 cache335.

Each GPC 208 may have an associated memory management unit (MMU) 320that is configured to map virtual addresses into physical addresses. Invarious embodiments, MMU 320 may reside either within GPC 208 or withinthe memory interface 214. The MMU 320 includes a set of page tableentries (PTEs) used to map a virtual address to a physical address of atile or memory page and optionally a cache line index. The MMU 320 mayinclude address translation lookaside buffers (TLB) or caches that mayreside within SMs 310, within one or more L1 caches, or within GPC 208.

In graphics and compute applications, GPC 208 may be configured suchthat each SM 310 is coupled to a texture unit 315 for performing texturemapping operations, such as determining texture sample positions,reading texture data, and filtering texture data.

In operation, each SM 310 transmits a processed task to workdistribution crossbar 330 in order to provide the processed task toanother GPC 208 for further processing or to store the processed task inan L2 cache (not shown), parallel processing memory 204, or systemmemory 104 via crossbar unit 210. In addition, a pre-raster operations(preROP) unit 325 is configured to receive data from SM 310, direct datato one or more raster operations (ROP) units within partition units 215,perform optimizations for color blending, organize pixel color data, andperform address translations.

It will be appreciated that the core architecture described herein isillustrative and that variations and modifications are possible. Amongother things, any number of processing units, such as SMs 310, textureunits 315, or preROP units 325, may be included within GPC 208. Further,as described above in conjunction with FIG. 2, PPU 202 may include anynumber of GPCs 208 that are configured to be functionally similar to oneanother so that execution behavior does not depend on which GPC 208receives a particular processing task. Further, each GPC 208 operatesindependently of the other GPCs 208 in PPU 202 to execute tasks for oneor more application programs. In view of the foregoing, persons ofordinary skill in the art will appreciate that the architecturedescribed in FIGS. 1-3A in no way limits the scope of the presentinvention.

Graphics Pipeline Architecture

FIG. 3B is a conceptual diagram of a graphics processing pipeline 350that may be implemented within PPU 202 of FIG. 2, according to oneembodiment of the present invention. As shown, the graphics processingpipeline 350 includes, without limitation, a primitive distributor (PD)355; a vertex attribute fetch unit (VAF) 360; a vertex, tessellation,geometry processing unit (VTG) 365; a viewport scale, cull, and clipunit (VPC) 370; a tiling unit 375, a setup unit (setup) 380, arasterizer (raster) 385; a fragment processing unit, also identified asa pixel shading unit (PS) 390, and a raster operations unit (ROP) 395.

The PD 355 collects vertex data associated with high-order surfaces,graphics primitives, and the like, from the front end 212 and transmitsthe vertex data to the VAF 360.

The VAF 360 retrieves vertex attributes associated with each of theincoming vertices from shared memory and stores the vertex data, alongwith the associated vertex attributes, into shared memory.

The VTG 365 is a programmable execution unit that is configured toexecute vertex shader programs, tessellation programs, and geometryprograms. These programs process the vertex data and vertex attributesreceived from the VAF 360, and produce graphics primitives, as well ascolor values, surface normal vectors, and transparency values at eachvertex for the graphics primitives for further processing within thegraphics processing pipeline 350. Although not explicitly shown, the VTG365 may include, in some embodiments, one or more of a vertex processingunit, a tessellation initialization processing unit, a task generationunit, a task distributor, a topology generation unit, a tessellationprocessing unit, and a geometry processing unit.

The vertex processing unit is a programmable execution unit that isconfigured to execute vertex shader programs, lighting and transformingvertex data as specified by the vertex shader programs. For example, thevertex processing unit may be programmed to transform the vertex datafrom an object-based coordinate representation (object space) to analternatively based coordinate system such as world space or normalizeddevice coordinates (NDC) space. The vertex processing unit may readvertex data and vertex attributes that is stored in shared memory by theVAF and may process the vertex data and vertex attributes. The vertexprocessing unit 415 stores processed vertices in shared memory.

The tessellation initialization processing unit is a programmableexecution unit that is configured to execute tessellation initializationshader programs. The tessellation initialization processing unitprocesses vertices produced by the vertex processing unit and generatesgraphics primitives known as patches. The tessellation initializationprocessing unit also generates various patch attributes. Thetessellation initialization processing unit then stores the patch dataand patch attributes in shared memory. In some embodiments, thetessellation initialization shader program may be called a hull shaderor a tessellation control shader.

The task generation unit retrieves data and attributes for vertices andpatches from shared memory. The task generation unit generates tasks forprocessing the vertices and patches for processing by later stages inthe graphics processing pipeline 350.

The task distributor redistributes the tasks produced by the taskgeneration unit. The tasks produced by the various instances of thevertex shader program and the tessellation initialization program mayvary significantly between one graphics processing pipeline 350 andanother. The task distributor redistributes these tasks such that eachgraphics processing pipeline 350 has approximately the same workloadduring later pipeline stages.

The topology generation unit retrieves tasks distributed by the taskdistributor. The topology generation unit indexes the vertices,including vertices associated with patches, and computes (U,V)coordinates for tessellation vertices and the indices that connect thetessellated vertices to form graphics primitives. The topologygeneration unit then stores the indexed vertices in shared memory.

The tessellation processing unit is a programmable execution unit thatis configured to execute tessellation shader programs. The tessellationprocessing unit reads input data from and writes output data to sharedmemory. This output data in shared memory is passed to the next shaderstage, the geometry processing unit 445 as input data. In someembodiments, the tessellation shader program may be called a domainshader or a tessellation evaluation shader.

The geometry processing unit is a programmable execution unit that isconfigured to execute geometry shader programs, thereby transforminggraphics primitives. Vertices are grouped to construct graphicsprimitives for processing, where graphics primitives include triangles,line segments, points, and the like. For example, the geometryprocessing unit may be programmed to subdivide the graphics primitivesinto one or more new graphics primitives and calculate parameters, suchas plane equation coefficients, that are used to rasterize the newgraphics primitives.

The geometry processing unit transmits the parameters and verticesspecifying new graphics primitives to the VPC 370. The geometryprocessing unit may read data that is stored in shared memory for use inprocessing the geometry data. The VPC 370 performs clipping, culling,perspective correction, and viewport transform to determine whichgraphics primitives are potentially viewable in the final rendered imageand which graphics primitives are not potentially viewable. The VPC 370then transmits processed graphics primitives to the tiling unit 375.

The tiling unit 375 is a graphics primitive sorting engine that residesbetween a world space pipeline 352 and a screen space pipeline 354, asfurther described herein. Graphics primitives are processed in the worldspace pipeline 352 and then transmitted to the tiling unit 375. Thescreen space is divided into cache tiles, where each cache tile isassociated with a portion of the screen space. For each graphicsprimitive, the tiling unit 375 identifies the set of cache tiles thatintersect with the graphics primitive, a process referred to herein as“tiling.” After tiling a certain number of graphics primitives, thetiling unit 375 processes the graphics primitives on a cache tile basis,where graphics primitives associated with a particular cache tile aretransmitted to the setup unit 380. The tiling unit 375 transmitsgraphics primitives to the setup unit 380 one cache tile at a time.Graphics primitives that intersect with multiple cache tiles aretypically processed once in the world space pipeline 352, but are thentransmitted multiple times to the screen space pipeline 354.

Such a technique improves cache memory locality during processing in thescreen space pipeline 354, where multiple memory operations associatedwith a first cache tile access a region of the L2 caches, or any othertechnically feasible cache memory, that may stay resident during screenspace processing of the first cache tile. Once the graphics primitivesassociated with the first cache tile are processed by the screen spacepipeline 354, the portion of the L2 caches associated with the firstcache tile may be flushed and the tiling unit may transmit graphicsprimitives associated with a second cache tile. Multiple memoryoperations associated with a second cache tile may then access theregion of the L2 caches that may stay resident during screen spaceprocessing of the second cache tile. Accordingly, the overall memorytraffic to the L2 caches and to the render targets may be reduced. Insome embodiments, the world space computation is performed once for agiven graphics primitive irrespective of the number of cache tiles inscreen space that intersects with the graphics primitive.

The setup unit 380 receives vertex data from the VPC 370 via the tilingunit 375 and calculates parameters associated with the graphicsprimitives, including, without limitation, edge equations, partial planeequations, and depth plane equations. The setup unit 380 then transmitsprocessed graphics primitives to rasterizer 385.

The rasterizer 385 scan converts the new graphics primitives andtransmits fragments and coverage data to the pixel shading unit 390.Additionally, the rasterizer 385 may be configured to perform z cullingand other z-based optimizations.

The pixel shading unit 390 is a programmable execution unit that isconfigured to execute fragment shader programs, transforming fragmentsreceived from the rasterizer 385, as specified by the fragment shaderprograms. Fragment shader programs may shade fragments at pixel-levelgranularity, where such shader programs may be called pixel shaderprograms. Alternatively, fragment shader programs may shade fragments atsample-level granularity, where each pixel includes multiple samples,and each sample represents a portion of a pixel. Alternatively, fragmentshader programs may shade fragments at any other technically feasiblegranularity, depending on the programmed sampling rate.

In various embodiments, the fragment processing unit 460 may beprogrammed to perform operations such as perspective correction, texturemapping, shading, blending, and the like, to produce shaded fragmentsthat are transmitted to the ROP 395. The pixel shading unit 390 may readdata that is stored in shared memory.

The ROP 395 is a processing unit that performs raster operations, suchas stencil, z test, blending, and the like, and transmits pixel data asprocessed graphics data for storage in graphics memory via the memoryinterface 214, where graphics memory is typically structured as one ormore render targets. The processed graphics data may be stored ingraphics memory, parallel processing memory 204, or system memory 104for display on display device 110 or for further processing by CPU 102or parallel processing subsystem 112. In some embodiments, the ROP 395is configured to compress z or color data that is written to memory anddecompress z or color data that is read from memory. In variousembodiments, the ROP 395 may be located in the memory interface 214, inthe GPCs 208, in the processing cluster array 230 outside of the GPCs,or in a separate unit (not shown) within the PPUs 202.

The graphics processing pipeline may be implemented by any one or moreprocessing elements within PPU 202. For example, one of the SMs 310 ofFIG. 3A could be configured to perform the functions of one or more ofthe VTG 365 and the pixel shading unit 390. The functions of the PD 355,the VAF 360, the VPC 450, the tiling unit 375, the setup unit 380, therasterizer 385, and the ROP 395 may also be performed by processingelements within a particular GPC 208 in conjunction with a correspondingpartition unit 215. Alternatively, graphics processing pipeline 350 maybe implemented using dedicated fixed-function processing elements forone or more of the functions listed above. In various embodiments, PPU202 may be configured to implement one or more graphics processingpipelines 350.

In some embodiments, the graphics processing pipeline 350 may be dividedinto a world space pipeline 352 and a screen space pipeline 354. Theworld space pipeline 352 processes graphics objects in 3D space, wherethe position of each graphics object is known relative to other graphicsobjects and relative to a 3D coordinate system. The screen spacepipeline 354 processes graphics objects that have been projected fromthe 3D coordinate system onto a 2D planar surface representing thesurface of the display device 110. For example, the world space pipeline352 could include pipeline stages in the graphics processing pipeline350 from the PD 355 through the VPC 370. The screen space pipeline 354could include pipeline stages in the graphics processing pipeline 350from the setup unit 380 through the ROP 395. The tiling unit 375 wouldfollow the last stage of the world space pipeline 352, namely, the VPC370. The tiling unit 375 would precede the first stage of the screenspace pipeline 354, namely, the setup unit 380.

In some embodiments, the world space pipeline 352 may be further dividedinto an alpha phase pipeline and a beta phase pipeline. For example, thealpha phase pipeline could include pipeline stages in the graphicsprocessing pipeline 350 from the PD 355 through the task generationunit. The beta phase pipeline could include pipeline stages in thegraphics processing pipeline 350 from the topology generation unitthrough the VPC 370. The graphics processing pipeline 350 performs afirst set of operations during processing in the alpha phase pipelineand a second set of operations during processing in the beta phasepipeline. As used herein, a set of operations is defined as one or moreinstructions executed by a single thread, by a thread group, or bymultiple thread groups acting in unison.

In a system with multiple graphics processing pipeline 350, the vertexdata and vertex attributes associated with a set of graphics objects maybe divided so that each graphics processing pipeline 350 hasapproximately the same amount of workload through the alpha phase. Alphaphase processing may significantly expand the amount of vertex data andvertex attributes, such that the amount of vertex data and vertexattributes produced by the task generation unit is significantly largerthan the amount of vertex data and vertex attributes processed by the PD355 and VAF 360. Further, the task generation unit associated with onegraphics processing pipeline 350 may produce a significantly greaterquantity of vertex data and vertex attributes than the task generationunit associated with another graphics processing pipeline 350, even incases where the two graphics processing pipelines 350 process the samequantity of attributes at the beginning of the alpha phase pipeline. Insuch cases, the task distributor redistributes the attributes producedby the alpha phase pipeline such that each graphics processing pipeline350 has approximately the same workload at the beginning of the betaphase pipeline.

Please note, as used herein, references to shared memory may include anyone or more technically feasible memories, including, withoutlimitation, a local memory shared by one or more SMs 310, or a memoryaccessible via the memory interface 214, such as a cache memory,parallel processing memory 204, or system memory 104. Please also note,as used herein, references to cache memory may include any one or moretechnically feasible memories, including, without limitation, an L1cache, an L1.5 cache, and the L2 caches.

Tiled Caching

FIG. 4 is a conceptual diagram of a cache tile 410(0) that the graphicsprocessing pipeline 350 of FIG. 3B may be configured to generate andprocess, according to one embodiment of the present invention. As shown,the cache tile 410(0) represents a portion of a screen space 400 and isdivided into multiple raster tiles 420.

The screen space 400 represents one or more memory buffers configured tostore rendered image data and other data transmitted by functional unitswithin the graphics processing pipeline 350. In some embodiments, theone or more memory buffers may be configured as one or more rendertargets. The screen space represents a memory buffer configured to storethe image rendered by the graphics processing pipeline. The screen space400 may be associated with any number of render targets, where eachrender target may be configured independently of other render targets toinclude any number of fields. Each field within a render target may beconfigured independently of other fields to include any number of bits.Each render target may include multiple picture elements (pixels), andeach pixel may, in turn, include multiple samples. In some embodiments,the size of each cache tile may be based on the size and configurationof the render targets associated with the screen space. In operation,once rendering completes, the pixels in the one or more render targetsmay be transmitted to a display device in order to display the renderedimage.

By way of example, a set of render targets for the screen space 400could include eight render targets. The first render target couldinclude four fields representing color, including red, green, and bluecomponent colors, and transparency information associated with acorresponding fragment. The second render target could include twofields representing depth and stencil information associated with thecorresponding fragment. The third render target could include threefields representing surface normal vector information, including anx-axis normal vector, a y-axis normal vector, and a z-axis normalvector, associated with the corresponding fragment. The remaining fiverender targets could be configured to store additional informationassociated with the corresponding fragment. Such configurations couldinclude storage for various information, including, without limitation,3D positional data, diffuse lighting information, and specular lightinginformation.

Each cache tile 410 represents a portion of the screen space 400. Forclarity, only five cache tiles 410(0)-410(4) are shown in FIG. 4. Insome embodiments, cache tiles may have an arbitrary size in X and Yscreen space. For example, if a cache tile were to reside in a cachememory that also is used to store other data, then the cache tile couldbe sized to consume only a specific portion of the cache memory. Thesize of a cache tile may be based on a number of factors, including, thequantity and configuration of the render targets associated with thescreen space 400, the quantity of samples per pixel, and whether thedata stored in the cache tile is compressed. As a general matter, acache tile is sized to increase the likelihood that the cache tile dataremains resident in the cache memory until all graphics primitivesassociated with the cache tile are fully processed.

The raster tiles 420 represent a portion of the cache tile 410(0). Asshown, the cache tile 410(0) includes sixteen raster tiles420(0)-420(15) arranged in an array that is four raster tiles 420 wideand four raster tiles 420 high. In systems that include multiple GPCs208, processing associated with a given cache tile 410(0) may be dividedamong the available GPCs 208. In the example shown, if the sixteenraster tiles of cache tile 410(0) were processed by four different GPCs208, then each GPC 208 could be assigned to process four of the sixteenraster tiles 420 in the cache tile 410(0). Specifically, the first GPC208 could be assigned to process raster tiles 420(0), 420(7), 420(10),and 420(13). The second GPC 208 could be assigned to process rastertiles 420(1), 420(4), 420(11), and 420(14). The third GPC 208 could beassigned to process raster tiles 420(2), 420(5), 420(8), and 420(15).The fourth GPC 208 would then be assigned to process raster tiles420(3), 420(6), 420(9), and 420(12). In other embodiments, theprocessing of the different raster tiles within a given cache tile maybe distributed among GPCs 208 or any other processing entities includedwithin computer system 100 in any technically feasible manner.

Tiling Unit Operation

FIG. 5 illustrates a graphics subsystem configured to implement cachetiling, according to one embodiment of the present invention. Thegraphics subsystem 500 illustrates several units that are describedabove with respect to FIG. 3B. As shown, the graphics subsystem 500includes a front end unit 212, a first world-space pipeline 352(0), asecond world-space pipeline 352(1), a crossbar unit 530 (“XBAR”), afirst tiling unit 575(0), a second tiling unit 575(1), a firstscreen-space pipeline 354(0), and a second screen-space pipeline 354(1).

The graphics subsystem 500 includes at least two instances of thescreen-space pipeline 354 and the world-space pipeline 352, forincreased performance. The graphics subsystem 500 also includes acrossbar unit 530 for transmitting work output from the firstworld-space pipeline 352(0) and the second world-space pipeline 352(1)to the first tiling unit 575(0) and the second tiling unit 575(1).Although depicted in FIG. 5 with two instances of the world-spacepipeline 352 and the screen-space pipeline 354, the teachings providedherein apply to graphics pipelines having any number of world-spacepipelines 352 and screen-space pipelines 354. Each of the screen-spacepipeline 354 and the world-space pipeline 352 are described in moredetail above with respect to FIG. 3B.

The functionality of the world-space pipelines 352 and the screen-spacepipelines 354 are implemented by processing entities such as generalprocessing clusters (GPC) 208, described above. In one embodiment, thefirst world-space pipeline 352(0) may be implemented in a first GPC208(0) and the second world-space pipeline 352(1) may be implemented ina second GPC 208(1). As a general matter, each screen-space pipeline 352may be implemented in a different GPC 208, and in a similar fashion,each world-space pipeline 354 may be implemented in a different GPC 208.Further, a given GPC 208 can implement a world-space pipeline 354 andalso a screen-space pipeline 352. For example, the first GPC 208(0) mayimplement both the first world-space pipeline 352(0) and the firstscreen-space pipeline 354(0). In embodiments that include more than onescreen-space pipeline 354, each screen-space pipeline 354 is associatedwith a different set of raster tiles 420 for any particular rendertarget. Again, each of the screen-space pipeline 354 and world-spacepipeline 352 are described in more detail above with respect to FIG. 3B.

Each of the pipeline units in the world-space pipelines 352 (i.e.,primitive distributor 355, vertex attribute fetch unit 360, vertex,tessellation, geometry processing unit 365, and viewport scale, cull,and clip unit 370) and in the screen-space pipelines 354 (i.e., setup380, rasterizer 385, pixel shader 390, and ROP 395) depicted in FIG. 5functions in a similar manner as described above with respect to FIGS.1-4.

A device driver 103 transmits instructions to the front end unit 212.The instructions include primitives and commands to bind render targets,arranged in application-programming-interface order (API order). APIorder is the order in which the device driver 103 specifies that thecommands should be executed and is typically specified by an applicationexecuting on CPU 102. For example, an application may specify that afirst primitive is to be drawn and then that a second primitive is to bedrawn. The application may also specify that certain work is to berendered to a particular render target, or that one or more rendertargets are to be bound.

When the front end unit 212 receives the instructions from the devicedriver 103, the front end unit 212 distributes tasks associated with theinstructions to the world-space pipelines 352 for processing. In oneembodiment, the front end unit 212 assigns tasks to the firstworld-space pipeline 352(0) and the second world-space pipeline 352(1)in round-robin order. For example, the front end unit 212 may transmittasks for a first batch of primitives associated with the instructionsto the first world-space pipeline 352(0) and tasks for a second batch ofprimitives associated with the instructions to the second world-spacepipeline 352(1).

Each of the first world-space pipeline 352(0) and second world-spacepipeline 352(1) processes tasks associated with the instructions, andgenerate primitives for processing by the first screen-space pipeline354(0) and the second screen-space pipeline 354(1). The firstworld-space pipeline 352 (0) and second world-space pipeline 352(1) eachinclude a bounding box generator unit (not shown) that determines towhich screen space pipeline—the first screen-space pipeline 354(0) orthe second screen-space pipeline 354(1)—each primitive should betransmitted. To make this determination, the bounding box generator unitgenerates bounding boxes for each primitive, and compares the boundingboxes to raster tiles 420. If a bounding box associated with a primitiveoverlaps one or more raster tiles associated with a particularscreen-space pipeline 354, then the bounding box generator unitdetermines that the primitive is to be transmitted to that screen-spacepipeline 354. A primitive may be transmitted to multiple screen-spacepipelines 354 if the primitive overlaps raster tiles 420 associated withmore than one screen-space pipeline 354. After the world-space pipelines352 generate the primitives, the world-space pipelines 352 transmit theprimitives to the crossbar unit 530, which transmits the primitives tothe corresponding tiling units 375 as specified by the bounding boxgenerator unit.

The tiling units 575 receive primitives from the crossbar unit 530. Eachtiling unit 575 accepts and stores these primitives until the tilingunit 575 decides to perform a flush operation. Each tiling unit 575decides to perform a flush operation when one or more resource countersmaintained by the tiling units 575 indicates that a resource hasexceeded a threshold. Each tiling unit 575 may also perform a flushoperation upon receiving a command from upstream in the graphicsprocessing pipeline 500 requesting that the tiling unit 575 perform aflush operation. Such a command is referred to herein as a“flush-tiling-unit command.” The device driver 103 may transmit theflush-tiling-unit command to the graphics processing pipeline 500 insituations that the device driver 103 deems appropriate.

Upon receiving primitives, a tiling unit 575 updates several resourcecounters associated with the primitives. The resource counters areconfigured to track the degree of utilization of various resourcesassociated with the primitives received by the tiling units 575.Resources are either global resources or local resources. Globalresources are pools of resources that are shared by all screen-spacepipelines 354 and world-space pipelines 352. Local resources areresources that not shared between screen-space pipelines 354 or betweenworld-space pipelines 352. Several examples of local and globalresources are now provided.

One type of local resource is a primitive storage space for storingprimitives in a tiling unit 575. Each tiling unit 575 includes aprimitive storage space that is maintained independently of primitivestorage space for other tiling units 575. When a tiling unit 575receives a primitive, some of the primitive storage space is occupied bythe primitive. Because only a limited amount of primitive storage spaceexists for each tiling unit 575, exceeding a threshold amount of storagespace in a particular tiling unit 575 causes the tiling unit 575 toperform a flush operation.

One type of global resource is a vertex attribute circular buffer. Thevertex attribute circular buffer includes circular buffer entries thatinclude vertex attributes. The vertex attribute circular buffer isavailable to units in the graphics subsystem 500 for reading vertexattributes associated with primitives. Each circular buffer entry in thevertex attribute circular buffer occupies a variable amount of storagespace. Each tiling unit 575 maintains a count of the amount of spaceoccupied by circular buffer entries associated with primitives in thetiling unit 575.

In one embodiment, the vertex attribute circular buffer may bestructured as a collection of smaller per-world-space-pipeline circularbuffers. Each per-world-space pipeline circular buffer is associatedwith a different world-space pipeline 352. If memory space associatedwith any of the per-world-space-pipeline circular buffers exceed athreshold value, then the associated tiling unit performs a flushoperation.

Another type of global resource is a pool of constant buffer tableindices. At the application-programming-interface level, an applicationprogrammer is permitted to associate constants with shader programs.Different shader programs may be associated with different constants.Each constant is a value that may be accessed while performingcomputations associated with the shader programs. The pool of constantbuffer table indices is a global resource by which constants areassociated with shader programs.

When a tiling unit 575 performs a flush operation, the tiling unit 575iterates through all of the cache tiles 410, and for each cache tile410, generates a cache tile batch that includes primitives that overlapthe cache tile 410, and transmits the cache tile batches to theassociated screen-space pipeline 354. Each tiling unit 575 is associatedwith a different screen-space pipeline 354. Thus, each tiling unit 575transmits cache tile batches to the associated screen-space pipeline354.

The tiling unit 575 transmits these cache tile batches to thescreen-space pipeline 354 associated with the tiling unit as the cachetile batches are generated. The tiling unit 575 continues to generateand transmit cache tile batches in this manner for all cache tiles 410associated with a render target. In one embodiment, the tiling unit 575determines which primitives overlap a cache tile 410 by comparing aborder of the cache tile 410 with bounding boxes associated with theprimitives and received from the bounding box unit.

The cache tile batches flow through the screen-space pipelines 354 inthe order in which the tiling unit 575 generates the cache tile batches.This ordering causes the units in the screen-space pipelines 354 toprocess the primitives in cache tile order. In other words, thescreen-space pipelines 354 process primitives that overlap a first cachetile, and then process primitives that overlap a second cache tile, andso on.

Conceptually, each cache tile batch can be thought of as beginning atthe point in time at which the tiling unit 575 began acceptingprimitives after the previous flush operation. In other words, eventhough the cache tile batches are transmitted to and processed by thescreen-space pipelines 354 sequentially, each cache tile batch logicallybegins at the same point in time. Of course, because the cache tilesgenerally do not overlap in screen space, sequential processing in thismanner generally produces the desired results.

As shown, graphics processing pipeline 500 includes count memories 555and accumulating memories 557. Count memories 555 are configured totrack a count associated with a particular event as work is processed bythe screen-space pipeline 354. For example, count memories 555 may beconfigured to track a number of pixels for which a specific operation isperformed by the pixel shader 390. The accumulating memories 557 areupdated in conjunction with the count memories 555 to provide eventcount reports to an external memory location included in an externalmemory unit, such as system memory 104 or a PP memory 204. Operation ofthe accumulating memories 557 in conjunction with the count memories 555is described in greater detail with respect to FIGS. 7-10.

The count memories 555 and accumulating memories 557 are depicted inFIG. 5 as being included in the pixel shaders 390. However, the countmemories 555 and accumulating memories 557 may be in other units, suchas the rasterizer 385 or the raster operations unit 395. The countmemories 555 may be configured to track an event count associated withthe unit in which the count memories are stored 555 or otherwiseassociated. For example, a count memory 555 stored in the rasteroperations unit 395 may be configured to track a number of pixels thatpass a z-test. Additionally, each screen-space pipeline 354 may includemore than one of each of the count memories 555 and accumulatingmemories 557, in different units or in the same units, each configuredto track a different event count. In some embodiments, the count memory555 and accumulating memory 557 is not physically stored in thecorresponding unit, but are still logically associated with that unit.

The count memories 555 and accumulating memories 557 are configured torespond to certain commands that flow through the screen-space pipeline354. One such command is a command to set the value of the count memory555 or the accumulating memory 557. Such a command may set the valuestored in the count memory 555 or the accumulating memory 557 to anyvalue, such as 0 or a value stored at another location. Another suchcommand is a report command. A report command specifies a particularevent count to record. When issued by the driver 103, a report commandtravels to the tiling unit 575.

In some embodiments, the driver 103 first transmits the report commandto front end 212, which transmits the report command to a screen-spacecircular buffer. Subsequently, the tiling unit 575 retrieves the reportcommand from the screen-space circular buffer at the correct point intime in application-programming-interface order (API order). API orderis the order in which the driver 103 transmits work, such as primitivesand commands, to the graphics processing pipeline 500. In otherembodiments, the driver 103 transmits the report command to front end212, which transmits the report command to the world-space pipeline 352.The world-space pipeline 352 transmits the report command to thecrossbar unit 530, which transmits the report command to each tilingunit 575. The tiling unit 575 inserts the report command in each cachetile batch in API order.

When the report command arrives at the unit in the screen-space pipeline354 that is associated with the event count specified by the reportcommand, the report command records the value stored in the count memory555 associated with that event count and travels through the rest of thescreen-space pipeline 354. When a command to clear the count memoryvalue 555 arrives at the unit in the screen-space pipeline 354, thatunit also clears the value in the count memory 555 (i.e, sets the valueto 0). When the report command, now storing the event count from thecount memory 555, arrives at the raster operations unit 395, the rasteroperations unit 395 forwards the report command to the front end unit212. The front end unit reads the value stored in the report command andperforms an atomic add operation to add the value to a value stored atan external memory location specified by the report command.

As described above, the tiling unit 575 receives primitives and a reportcommand and generates cache tile batches. Each cache tile batch includesprimitives that overlap the cache tile associated with the cache tilebatch, as well as the report command. Within each cache tile batch, theprimitives and report command are organized inapplication-programming-interface order (API order). API order is theorder in which the commands associated with the primitives and thereport command are received by the driver 103.

In the tiling architecture implemented in the graphics processingpipeline 500, including only the report command in each cache tilebatch, without more, generally does not produce desired event countreports. An explanation of what event count reports are produced whenonly the report command is included in each cache tile batch and whythose even count reports are unsatisfactory is provided below inconjunction with FIG. 6. FIGS. 7-10 illustrate additional commands thatthe tiling unit 575 includes in the cache tile batches in order toproduce the desired event count results.

Managing Event Counts Reports in a Cache Tiling Architecture

FIG. 6 is a workflow diagram 600 conceptually illustrating cache tilebatches produced by a tiling unit 575, according to one embodiment ofthe present invention. The workflow diagram 600 depicts cache tilebatches 602 produced as the result of a flush operation, with the firstcache tile batch 602(0) being the earliest cache tile batch produced andthe last cache tile batch 602(N−1) being the final cache tile batchproduced. Cache tile batch 602(1) is an intermediate cache tile batch602. Other intermediate cache tile batches 602 are produced but are notdepicted in FIG. 6.

As shown, each of the cache tile batches 602 includes a first set ofprimitives 604, labeled “A(X)”, a report command 606, and a second setof primitives 608, labeled “B(X).” The first set of primitives 604,report command 606, and second set of primitives 608 are included ineach cache tile batch in API order. The first set of primitives 604 alsoincludes a command to clear the value stored in the count memory 555 tozero after executing the report command 606. After generating the cachetile batches, the tiling unit 575 transmits the cache tile batches tothe screen-space pipeline 354 for processing. Workflow progression line620 illustrates the order in which the cache tile batches 602 areprocessed by the screen-space pipeline.

The first cache tile batch 602(0) includes first set of primitives604(0), which are processed by the screen-space pipeline 354. As thescreen-space pipeline 354 processes the first set of primitives 604(0),the count memory 555 is updated to reflect an event count. When thepixel shader 390 (i.e., the unit associated with the count memory 555)receives the report command 606(0), the pixel shader 390 stores thevalue stored in the count memory 555 in the report command 606(0) andforwards the report command down the screen-space pipeline 354. Thepixel shader 390 also executes the command to clear the count memoryvalue 555, which clears the value stored in the count memory 555 to 0.

When the report command arrives at the front end unit 212, the front endunit 212 performs an atomic add operation on the memory locationspecified by the report command. The atomic add operation adds the valuespecified by the count memory 555 to the specified memory location. Asdescribed above, the memory location is in an external memory unit, suchas system memory 104 or PP memory 204.

Because the count memory 555 is updated by work that flows through thescreen-space pipeline 354, regardless of which cache tile the work isincluded in, the count memory 555 reflects work associated with thefirst set of primitives 604(0), as well as work that is processed by thescreen-space pipeline 354 prior to receiving the first cache tile batch602(0). Therefore, the value stored in the count memory 555 when thereport command 606(0) arrives at the pixel shader 390 includes an“initial value I”—reflective of work completed prior to the first cachetile batch 602(0)—as well as the value A(0), reflective of workassociated with the first set of primitives 604(0). The report command606(0) thus adds the value “I+A(0)” to the memory location specified bythe report command 606(0). The value stored in the memory location isnow I₀+I+A(0), where I₀ is an initial value stored at the memorylocation.

After the pixel shader 390 receives the report command 606(0), the pixelshader 390 receives and processes the second set of primitives 608(0).When the pixel shader 390 processes the second set of primitives 608(0),the pixel shader 390 updates the value stored in the count memory 555.Thus, at the end of the first cache tile batch 602(0), the value in thecount memory 555 stores a value associated with the second set ofprimitives 608(0), which is B(0).

After receiving the second set of primitives 608(0), the pixel shader390 receives a first set of primitives 604(1) in the second cache tilebatch 602(1). When the pixel shader 390 processes the first set ofprimitives 604(1), the pixel shader updates the value stored in thecount memory 555 to reflect the work associated with the first set ofprimitives 604(1). When the pixel shader 390 receives the second reportcommand 606(1), the count memory 555 stores the value of B(0)+A(1). Thepixel shader 390 includes this value in the report command 606(1) andforwards the report command 606(1) down the screen-space pipeline 354.The pixel shader 390 also clears the value in the count memory 555 to 0.The front end unit 212 adds the value stored in the report command606(1) to the memory location specified by the report command 606(1),which is the same memory location as specified by the first reportcommand 606(0), and by all other report commands 606 depicted in FIG. 6.The value stored in the memory location is now I₀+I+A(0)+B(0)+A(1).

Processing as described above continues for all cache tile batches 602depicted in FIG. 6, until the final cache tile batch 602(N−1). When thepixel shader 390 processes the first set of primitives 604(N−1) includedin the final cache tile batch 602(N−1), the pixel shader 390 updates thecount memory 555 to the appropriate value. The report command 606(N−1)records this value. The pixel shader 390 also clears the count memory555. When the report command 606(N−1) arrives at front end 212, frontend 212 adds the value in the report command 606(N−1) to the memorylocation. The value stored in the memory location is nowI₀+I+A(0)+B(0)+A(1)+ . . . +B(N−2)+A(N−1).

As these results show, the value stored at the memory location at theend of processing the cache tile batches 602 illustrated in FIG. 6 isnot the desired result. Logically, the report commands 606 are insertedinto each cache tile after a first set of primitives A, but before asecond set of primitives B. Thus, the desired result for the reportcommand 606 would be to include all work associated with A, but toinclude none of the work associated with B. However, the value stored inthe memory location includes work associated with both A and B. Thisdiscrepancy is caused by the fact that although all work associated withA is “logically” processed first, in actuality, the work is processed incache tile order. Thus, the count memory 555 records values in thisorder, which causes the discrepancy.

To avoid unsatisfactory outcomes, like those described above, the tilingunit 575 includes additional operations with each cache tile batch inorder to record the desired results in the external memory location. Theadditional operations generally involve manipulating the values storedin the count memory 555 and the accumulating memory 557 to track valuesacross the cache tile batches in a beneficial manner. These additionaloperations are discussed in more detail in FIGS. 7-10.

FIG. 7 conceptually illustrates a sequence 700 of operations associatedwith the tiling unit 575, for managing event counts, according to oneembodiment of the present invention. As shown, the sequence 700 ofoperations includes work 701 received by the tiling unit 575, and cachetile batches 710 generated by the tiling unit and provided to thescreen-space pipeline 354.

The tiling unit 575 receives the work 701, which includes a first set ofprimitives 702, a report command 704, and a second set of primitives706. The tiling unit 575 generates cache tile batches 710 and outputsthe cache tile batches to the screen-space pipeline 354 for processing.The cache tile batches 710 each include primitives that overlap aparticular cache tile, report commands, and commands to modify the valuestored in the count memory 555 and the accumulating memory 557.

A first cache tile batch 710(0) includes a first set of primitives712(0) (labeled “Work A”), which includes primitives included in work A702 that overlap the cache tile associated with the first cache tilebatch 710(0). After the first set of primitives 712(0), the first cachetile batch includes a report command 714(0). The tiling unit 575includes the report command 714 at a location in the cache tile batch710(0) that corresponds to the location of the report command 704 inwork 701 received by the tiling unit 575. The report command 714(0)records the value stored in the count memory 555 and causes the pixelshader 390 to set the value in the count memory 555 to zero. The reportcommand flows through the screen-space pipeline 354. When the reportcommand 714(0) arrives at ROP 395, ROP 395 forwards the report command714(0) to the front end unit 212, which causes the value stored in thereport command 714(0) to be added to a memory location specified by thereport command 714(0). In some embodiments, the value is addedatomically, to accommodate parallel processing.

After the report command 714(0), the first cache tile batch 710(0)includes a second set of primitives 716(0) (labeled “Work B”), whichincludes primitives included in work B 706 that overlap the cache tileassociated with the first cache tile batch 710(0). After the second setof primitives 716(0), the first cache tile batch 710(0) includes acommand to modify the accumulating memory 557 and the count memory 555.The command to modify the accumulating memory 557 is configured to setthe value stored in the accumulating memory 557 to be equal to the valuestored in the count memory 555. The first cache tile batch 710(0) alsoincludes a command to reset the count memory 555 to zero after thecommand to set the value in the accumulating memory 557.

The second cache tile batch 710(1), which is termed an “intermediatecache tile batch” due to being neither the first cache tile batch 710(0)nor the last tile batch 710(N−1) includes the following work. First, thesecond cache tile batch 710(1) includes a first set of primitives 712(1)(labeled “Work A”), which includes primitives included in work A 702that overlap the cache tile associated with the second cache tile batch710(1). After the first set of primitives 712(1), the second cache tilebatch includes a report command 714(1). The report command 714(1)records the value stored in the count memory 555 and causes the pixelshader 390 to set the value in the count memory 555 to zero. Asdescribed above with respect to the first cache tile batch 710(0), thereport command flows through the screen-space pipeline 354 and causesthe front end unit 212 to add the value in the report command 714(1) tothe value in the memory location specified by the report command 714(1).The memory location for the report command 714(1) is the same as thememory location for the report command 714(0), and for all other reportcommands 714(X) in the other cache tile batches 710 generated by thetiling unit 575 as a result of receiving work 701.

After the report command 714(1), the second cache tile batch 710(1)includes a second set of primitives 716(1) (labeled “Work B”), whichincludes primitives included in work B 706 that overlap the cache tileassociated with the second cache tile batch 710(1). After the second setof primitives 716(1), the second cache tile batch 710(1) includes acommand to modify the accumulating memory 557 and the count memory 555.The command to modify the accumulating memory 557 is configured to addthe value stored in the count memory 555 to the value stored in theaccumulating memory 557. The second cache tile batch 710(1) alsoincludes a command to reset the count memory 555 to zero after thecommand to set the value in the accumulating memory 557. The command tomodify the accumulating memory 557 for the second cache tile batch710(1) is slightly different than the command to modify the accumulatingmemory 557 for the first cache tile batch 710(0). More specifically, thecommand to modify the accumulating memory 557 for the second cache tilebatch 710(1) adds the value stored in the count memory 555 to the valuestored in the accumulating memory 557, instead of simply setting thevalue of the accumulating memory 557 to be equal to the value stored inthe count memory 555. Other intermediate cache tile batches 710 includecommands similar to the commands included in the second cache tile batch710(1).

The final cache tile batch 710(N−1) includes the following work. First,the final cache tile batch 710(N−1) includes a first set of primitives712(N−1) (labeled “Work A”), which includes primitives included in workA 702 that overlap the cache tile associated with the final cache tilebatch 710(N−1). After the first set of primitives 712(N−1), the finalcache tile batch includes a report command 714(N−1). The report command714(N−1) records the value stored in the count memory 555 and causes thepixel shader 390 to set the value in the count memory 555 to zero. Asdescribed above with respect to the first cache tile batch 710(0) andthe second cache tile batch 710(1), the report command flows through thescreen-space pipeline 354 and causes the front end unit 212 to add thevalue in the report command 714(N−1) to the value in the memory locationspecified by the report command 714(N−1). As described above, the memorylocation for the report command 714(N−1) is the same as the memorylocation for the report command 714(0) and the report command 714(1).

After the report command 714(N−1), the final cache tile batch 710(N−1)includes a second set of primitives 716(N−1) (labeled “Work B”), whichincludes primitives included in work B 706 that overlap the cache tileassociated with the final cache tile batch 710(N−1). After the secondset of primitives 716(N−1), the final cache tile batch 710(N−1) includesa command to modify the accumulating memory 557 and the count memory555. As with the command to modify the accumulating memory in the secondcache tile batch 710(1), the command to modify the accumulating memory557 in the final cache tile batch 710(N-1) is configured to add thevalue stored in the count memory 555 to the value stored in theaccumulating memory 557. The final cache tile batch 710(N−1) alsoincludes a command to set the value stored in the count memory 555 to beequal to the value stored in the accumulating memory 557. The purpose ofthis command is to cause the count memory 555 to store the “carryover”from the current flush operation. This carryover is reflective of theevent count for all of Work B processed for all cache tile batches 710.If a subsequent flush operation includes another report command, thenthis carryover is added to the value calculated for the subsequent flushoperation in order to produce the desired results.

Although the examples provided in FIG. 6 depict each cache tile batch asincluding primitives corresponding to both work A 702 and work B 706,some cache tile batches may include no primitives corresponding toeither work A 702 or work B 706, or both. In such cases, the stepsdescribed above still produce the desired count results. The tiling unit575 simply inserts the report commands 714 and accumulate commands 718in API order.

In some flush operations, no report commands may be included in the workreceived by the tiling unit 575. In such cases, the count memory 555simply accumulates counts for the events that occur for all of the cachetile batches for such flush operations. If a report command is includedin a subsequent flush operation, then that report command producesdesired results because the report commands are configured to reportevent counts accumulated since a previous report command.

In some flush operations, multiple report commands 704 are included. Insuch cases, the tiling unit 575 inserts a corresponding report command714 for each of the report commands 704. Each of the different reportcommands 704 received by the tiling unit 575 specifies a differentexternal memory address. Therefore, the different report commands 714accumulate values in different memory addresses. (Of course, each of thereport commands 714 replicated across cache tile batches 710 thatcorrespond to a single report command 704 specifies the same memoryaddress. However, report commands 714 that correspond to differentreport commands 704 received by the tiliing unit 575 specify differentmemory addresses). An example of multiple report commands 704 includedin a single flush operation is described with respect to FIG. 9.

Several example workflow sequences are now described to illustrateoperation of the tiling unit 575 for generating event counts. FIG. 8illustrates a workflow depicting a single flush operation and FIG. 9illustrates a workflow depicting two flush operations.

FIG. 8 is a workflow diagram 800 conceptually illustrating workassociated with cache tile batches produced by a tiling unit 575 for asingle flush operation, according to one embodiment of the presentinvention. The workflow diagram 800 depicts a sequence of workassociated with cache tile batches 802 produced as the result of a flushoperation. The first cache tile batch 802(0) is the earliest cache tilebatch, the second cache tile batch 802(1) is an intermediate cache tilebatch, and the last cache tile batch 802(N−1) is the final cache tilebatch produced. Other intermediate cache tile batches 802 are producedbut not depicted in FIG. 8. Several sequence checkpoints 810 areindicated in the workflow diagram 800. The sequence checkpoints 810indicate points in the workflow sequence 800 at which the accumulatingmemory 557 and memory location associated with the command report areupdated. Workflow line 813 indicates the order of processing of thecache tile batches 802.

The report commands 806 are similar to the report commands 714 describedwith respect to FIG. 7. The accumulate commands 809 are similar to thecommands to modify the count memory 555 and the accumulating memory 557,discussed above with respect to FIG. 7. Table 1, provided below, depictsthe values of the external memory location, the count memory, and theaccumulating memory at the various checkpoints.

TABLE 1 Values of various memories at different checkpoints CountAccumulating External Memory Memory Memory Location Checkpoint 810(0) 0— I₀ + A(0) Checkpoint 812(0) 0 B(0) I₀ + A(0) Checkpoint 810(1) 0 B(0)I₀ + A(0) + A(1) Checkpoint 812(1) 0 B(0) + B(1) I₀ + A(0) + A(1)Checkpoint 810(N-1) 0 B(0) + B(1) I₀ + A(0) + A(1) + . . . + A(N-1)Checkpoint 812(N-1) B(0) + B(1) + . . . + B(0) + B(1) + . . . + I₀ +A(0) + B(N-1) B(N-1) A(1) + . . . + A(N-1)

As shown in Table 1, the accumulating memory accumulates the eventcounts for the work after the report request 806 (i.e., all of the eventcounts associated with “A”). The external memory location accumulatesthe value for the work prior to the report request 806. I₀ includes twocomponents. First, I₀ includes the value that is previously stored inthe external memory location, if any. The driver 103 may choose toinitialize this value to zero before generating the report request.Second, I₀ includes the value stored in the count memory 555 fromprevious flush operations. As described above, this “carry-over”represents event counts from previous flush operations. The value storedin the accumulating memory 557 at checkpoint 810(0) is irrelevantbecause that value is not examined or included in any operationsassociated with the report requests 806 or accumulate commands 809 andis overwritten. The accumulating memory 557 is first written to in thefirst accumulate command 809(0) associated with the first cache tilebatch 802(0).

FIG. 9 is a workflow diagram 900 conceptually illustrating workassociated with cache tile batches produced by a tiling unit 575 for twoflush operations, according to one embodiment of the present invention.The workflow diagram 900 is similar to the workflow diagram 800, exceptthat workflow diagram 900 depicts two flush operations, and that in thefirst flush operation, two report requests are provided. In the firstflush operation, cache tile batches 902 are generated. In the secondflush operation, cache tile batches 919 are generated.

In cache tile batches 902, report command 906 requests a report forevent counts prior to report command 906 in API order. Similarly, reportcommand 910 requests a report for event counts after report 906, butprior to report 910, in API order. Finally, report 916 requests a reportfor event counts after report 910, but prior to report 916. Each ofreport 906, report 910, and report 916 are associated with differentexternal memory locations and record their respective values to thosedifferent external memory locations.

As with FIG. 8, sequence checkpoints 920, 922, 924, 926, and 928indicate points in the workflow sequence 900 at which the accumulatingmemory 557, and external memory locations associated with the commandreports are updated. Table 2, provided below, depicts the values of theexternal memory locations, the count memory, and the accumulating memoryat the various checkpoints. External memory location 1 is associatedwith report 906. External memory location 2 is associated with report910. External memory location 3 is associated with report 912. Forsimplicity, each of the external memory locations depicted in Table 2 isassumed to be initialized to “0” by the driver 103. Workflow order line917 indicates the order of processing of the cache tile batches 902 andthe cache tile batches 919.

TABLE 2 Values of various memories at different checkpoints ExternalExternal External Count Accumulating Memory Memory Memory Memory MemoryLocation 1 Location 2 Location 3 Checkpoint 920(0) 0 — I₁ + A(0) 0 0Checkpoint 922(0) 0 — I₁ + A(0) B(0) 0 Checkpoint 924(0) 0 C1(0) I₁ +A(0) B(0) 0 Checkpoint 920(1)) 0 C1(0) I₁ + A(0) + A(1) B(0) 0Checkpoint 922(1) 0 C1(0) I₁ + A(0) + A(1) B(0) + B(1) 0 Checkpoint924(1) 0 C1(0) + C1(1) I₁ + A(0) + A(1) B(0) + B(1) 0 Checkpoint920(N-1) 0 C1(0) + C1(1) + . . . + I₁ + A(0) + B(0) + B(1) + . . . + 0C1(N-2) A(1) + . . . + A(N-1) B(N-2) Checkpoint 922(N-1) 0 C1(0) +C1(1) + . . . + I₁ + A(0) + B(0) + B(1) + . . . + 0 C1(N-2) A(1) + . .. + A(N-1) B(N-1) Checkpoint 924(N-1) C1(0) + C1(1) + . . . + C1(0) +C1(1) + . . . + I₁ + A(0) + B(0) + B(1) + . . . + 0 C1(N-1) C1(N-1)A(1) + . . . + A(N-1) B(N-1) Checkpoint 926(0) 0 C1(0) + C1(1) + . . . +I₁ + A(0) + B(0) + B(1) + . . . + C1(0) + C1(1) + . . . + C1(N-1) A(1) +. . . + A(N-1) B(N-1) C1(N-1) + C2(0) Checkpoint 928(0) 0 D(0) I₁ +A(0) + B(0) + B(1) + . . . + C1(0) + C1(1) + . . . + A(1) + . . . +A(N-1) B(N-1) C1(N-1) + C2(0) Checkpoint 926(1) 0 D(0) I₁ + A(0) +B(0) + B(1) + . . . + C1(0) + C1(1) + . . . + A(1) + . . . +A(N-1)B(N-1) C1(N-1) + C2(0) + C2(1) Checkpoint 928(1) 0 D(0) + D(1) I₁ +A(0) + B(0) + B(1) + . . . + C1(0) + C1(1) + . . . + A(1) + . . . +A(N-1) B(N-1) C1(N-1) + C2(0) + C2(1) Checkpoint 926(N-1) 0 D(0) +D(1) + . . . + I₁ + A(0) + B(0) + B(1) + . . . + C1(0) + C1(1) + . . . +D(N-2) A(1) + . . . + A(N-1) B(N-1) C1(N-1) + C2(0) + C2(1) + . . . +C2(N-1) Checkpoint 928(N-1) D(0) + D(1) + . . . + D(0) + D(1) + . . . +I₁ + A(0) + B(0) + B(1) + . . . + C1(0) + C1(1) + . . . + D(N-1) D(N-1)A(1) + . . . + A(N-1) B(N-1) C1(N-1) + C2(0) + C2(1) + . . . + C2(N-1)

As can be seen, the various external memories accumulate values fortheir respective subsets of work. The external memory location 1includes a sum of all of the “A” values (plus previous work reflected inI₁). I₁ includes the “carryover” stored in count memory 555 fromprevious flush operation(s). The external memory location 2 includes asum of all of the “B” values. The external memory location 3 includes asum of all of the “C” values, including the “C1” values and the “C2”values. At the end of the first flush operation, the sum for the Clvalues is carried over to the second flush operation in the count memory555. Thus, the report 916 generates results reflecting counts from boththe C1 work and the C2 work. This is the desired result, since thereport commands 916 record event counts since the previous reportcommand 910.

FIG. 10 is a flow diagram of method steps for recording event counts ina tile-based architecture, according to one embodiment of the presentinvention. Although the method steps are described in conjunction withthe system of FIGS. 1-9, persons skilled in the art will understand thatany system configured to perform the method steps, in any order, fallswithin the scope of the present invention.

As shown, a method 1000 begins in step 1002, where the tiling unit 575receives primitives and one or more report requests, and the tiling unit575 performs a flush operation. In step 1004, the tiling unit 575 setsthe next cache tile as the current cache tile. At the beginning of theflush operation, the “next” cache tile is the first cache tile for aparticular render target. In step 1006, the tiling unit 575 generates acache tile batch that includes the primitives that overlap the currentcache tile. In step 1008, the tiling unit 575 determines if the currentcache tile is the first cache tile for a particular render target. Ifthe current cache tile is the first cache tile for a particular rendertarget, then the method proceeds to step 1010. In step 1010, the tilingunit 575 includes a command to set an accumulating memory to be equal toa count memory at the end of the cache tile batch. The tiling unit 575also includes a command to clear the count memory at the end of thecache tile batch. After step 1010, the method proceeds to step 1018.

Referring back to step 1008, if the current cache tile is not the firstcache tile, then the method proceeds to step 1012. In step 1012, thetiling unit 575 determines whether the current cache tile is anintermediate cache tile. If the current cache tile is an intermediatecache tile, then the method proceeds to step 1014. In step 1014, thetiling unit 575 includes a command to set the value of an accumulatingmemory to be equal to the value in a count memory plus the value in theaccumulating memory at the end of the cache tile batch. The tiling unit575 also includes a command to clear the count memory at the end of thecache tile batch. After step 1014, the method proceeds to step 1018.

Referring back to step 1012, if the current cache tile is not anintermediate cache tile, then the current cache tile is a final cachetile, and the method proceeds to step 1016. In step 1016, the tilingunit 575 includes a command to set the value of an accumulating memoryto be equal to the value in a count memory plus the value in theaccumulating memory at the end of the cache tile batch. The tiling unit575 also includes a command to set the value of the count memory to beequal to the value stored in the accumulating memory at the end of thecache tile batch. After step 1016, the method proceeds to step 1018.

In step 1018, for each report request received by the tiling unit 575,the tiling unit 575 includes a command to add the value in the countmemory to an external memory, at a location in the cache tile batchcorresponding to the location of the report request. In step 1020, thetiling unit 575 transmits the cache tile batch to a screen-spacepipeline 354 for processing. In step 1022, the tiling unit 575determines whether there are more cache tiles left to process. If thereare more cache tiles, then the method returns to step 1004. If there arenot more cache tiles to process, then the method proceeds to step 1024,in which the tiling unit 575 waits for the next flush operation.

In sum, a screen-space pipeline includes a unit configured to record anevent count. The unit is associated with a count memory and anaccumulator memory. The count memory is configured to track the eventcount. The tiling unit receives work and a request for an event count.When the tiling unit reorganizes work and generates cache tile batchesfor transmission to the screen-space pipeline, the tiling unit includescertain commands in the cache tile batches that are configured to updatethe count memory, the accumulator memory, and an external memory torecord the event count.

In a first cache tile batch, the tiling unit includes a command to addthe value in the count memory to an external memory address specified bythe event count request. The tiling unit also includes a command toreset the count memory to zero. The command to set the external memoryaddress and to reset the count memory are included in the first cachetile batch at a point corresponding to the request for the event count.The tiling unit also includes at the end of the first cache tile batch acommand to set the accumulator memory to be equal to the value in thecount memory and to set the count memory to zero.

In each intermediate cache tile batch, the tiling unit includes acommand to add the value in the count memory to the external memoryaddress. The tiling unit also includes a command to reset the countmemory to zero in each intermediate cache tile batch. The tiling unitincludes the command to set the value in the external memory address andto reset the count memory at the point in the intermediate cache tilebatch corresponding to the request for the event count. The tiling unitalso includes at the end of each intermediate cache tile batch a commandto add the value in the count memory to the value in the accumulatormemory and to set the count memory to zero.

Finally, in a final cache tile batch, the tiling unit includes a commandto add the value in the count memory to the external memory address. Thetiling unit also includes a command to reset the count memory to zero inthe final cache tile batch. The tiling unit includes the command to setthe external memory address and the command to reset the count memory atthe point in the final cache tile batch corresponding to the request forthe event count. The tiling unit also includes at the end of the finalcache tile batch a command to add the value in the count memory to thevalue in the accumulator memory and to set the count memory to be equalto the value in the accumulator memory

One advantage of the disclosed approach is that event counts aregenerated in a tiling architecture having desired results. Anotheradvantage is that multiple event counts may be included in each flushoperation. An additional advantage is that the report commands trackvalues across different flush operations.

One embodiment of the invention may be implemented as a program productfor use with a computer system. The program(s) of the program productdefine functions of the embodiments (including the methods describedherein) and can be contained on a variety of computer-readable storagemedia. Illustrative computer-readable storage media include, but are notlimited to: (i) non-writable storage media (e.g., read-only memorydevices within a computer such as compact disc read only memory (CD-ROM)disks readable by a CD-ROM drive, flash memory, read only memory (ROM)chips or any type of solid-state non-volatile semiconductor memory) onwhich information is permanently stored; and (ii) writable storage media(e.g., floppy disks within a diskette drive or hard-disk drive or anytype of solid-state random-access semiconductor memory) on whichalterable information is stored.

The invention has been described above with reference to specificembodiments. Persons of ordinary skill in the art, however, willunderstand that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The foregoing description and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

Therefore, the scope of embodiments of the present invention is setforth in the claims that follow.

We claim:
 1. A graphics processing system, comprising: a screen-spacepipeline that includes a count memory and an accumulating memory; and atiling unit that causes the screen-space pipeline to increment a valuestored at an external memory address by a first value stored in thecount memory when a first unit has completed processing a first set ofprimitives that overlap a first cache tile, and causes the screen-spacepipeline to update the accumulating memory to reflect a second valuestored in the count memory when the first unit has completed processinga second set of primitives that overlap the first cache tile.
 2. Thegraphics processing system of claim 1, wherein the tiling unit receivesa first plurality of primitives that includes the first set ofprimitives, receives a second plurality of primitives that includes thesecond set of primitives, determines that the first set of primitivesoverlaps the first cache tile, and determines that the second set ofprimitives overlaps the first cache tile.
 3. The graphics processingsystem of claim 1, wherein the tiling unit receives a report request fora final count value associated with a first plurality of primitives thatincludes the first set of primitives.
 4. The graphics processing systemof claim 1, wherein the tiling unit transmits the first set ofprimitives, the second set of primitives, and a first set of commands tothe screen-space pipeline for processing, wherein the first set ofcommands includes a first command that causes the screen-space pipelineto increment the value stored at the external memory address afterprocessing the first command.
 5. The graphics processing system of claim4, wherein the first set of commands further includes a second commandthat causes the accumulating memory to store the second value stored inthe count memory when the first unit has completed processing the secondset of primitives.
 6. The graphics processing system of claim 5, whereinthe first set of commands further includes a third command that causesthe count memory to be reset after the second command is processed. 7.The graphics processing system of claim 4, wherein the first set ofcommands further includes a second command that causes the second valueto be added to the accumulating memory when the first unit has completedprocessing the second set of primitives.
 8. The graphics processingsystem of claim 7, wherein the first set of commands further includes athird command that causes the count memory to be reset after the secondcommand is processed.
 9. The graphics processing system of claim 4,wherein the first set of commands further includes a second command thatcauses the second value to be added to the accumulating memory when thefirst unit has completed processing the second set of primitives, andthe first set of commands further includes a third command that causesthe count memory to store a value equal to a value stored in theaccumulating memory after the second command is processed.
 10. Thegraphics processing system of claim 1, wherein at least one primitive inthe first set of primitives and at least one primitive in the second setof primitives cause the first unit to detect the event type andincrement the count memory.
 11. A computing device, comprising: amemory; and a graphics processing system that is coupled to the memoryand includes: a screen-space pipeline having a count memory and anaccumulating memory; and a tiling unit that causes the screen-spacepipeline to increment a value stored at an external memory address by afirst value stored in the count memory when a first unit has completedprocessing a first set of primitives that overlap a first cache tile,and causes the screen-space pipeline to update the accumulating memoryto reflect a second value stored in the count memory when the first unithas completed processing a second set of primitives that overlap thefirst cache tile.
 12. The computing device of claim 11, wherein thetiling unit receives a first plurality of primitives that includes thefirst set of primitives, receives a second plurality of primitives thatincludes the second set of primitives, determines that the first set ofprimitives overlaps the first cache tile, and determines that the secondset of primitives overlaps the first cache tile.
 13. The computingdevice of claim 11, wherein the tiling unit receives a report requestfor a final count value associated with a first plurality of primitivesthat includes the first set of primitives.
 14. The computing device ofclaim 11, wherein the tiling unit transmits the first set of primitives,the second set of primitives, and a first set of commands to thescreen-space pipeline for processing, wherein the first set of commandsincludes a first command that causes the screen-space pipeline toincrement the value stored at the external memory address afterprocessing the first command.
 15. The computing device of claim 14,wherein the first set of commands further includes a second command thatcauses the accumulating memory to store the second value stored in thecount memory when the first unit has completed processing the second setof primitives.
 16. The computing device of claim 15, wherein the firstset of commands further includes a third command that causes the countmemory to be reset after the second command is processed.
 17. Thecomputing device of claim 14, wherein the first set of commands furtherincludes a second command that causes the second value to be added tothe accumulating memory when the first unit has completed processing thesecond set of primitives.
 18. The computing device of claim 17, whereinthe first set of commands further includes a third command that causesthe count memory to be reset after the second command is processed. 19.The computing device of claim 14, wherein the first set of commandsfurther includes a second command that causes the second value to beadded to the accumulating memory when the first unit has completedprocessing the second set of primitives, and the first set of commandsfurther includes a third command that causes the count memory to store avalue equal to a value stored in the accumulating memory after thesecond command is processed.
 20. The computing device of claim 11,wherein at least one primitive in the first set of primitives and atleast one primitive in the second set of primitives cause the first unitto detect the event type and increment the count memory.
 21. Acomputer-implemented method, comprising: causing a screen-space pipelineto increment a value stored at an external memory address by a firstvalue stored in a count memory when a first unit included in thescreen-space pipeline and associated with the count memory has completeprocessing a first set of primitives that overlap a first cache tile;and causing the screen-space pipeline to update an accumulating memoryassociated with the first unit to reflect a second value stored in thecount memory when the first unit has completed processing a second setof primitives that overlap the first cache tile.
 22. Thecomputer-implemented method of claim 20, wherein at least one primitivein the first set of primitives and at least one primitive in the secondset of primitives cause the first unit to detect the event type andincrement the count memory.
 23. The computer-implemented method of claim20, further comprising receiving a first plurality of primitives thatincludes the primitives in the first set of primitives, receiving asecond plurality of primitives that includes the primitives in thesecond set of primitives, determining that the first set of primitivesoverlaps the first cache tile, and determining that the second set ofprimitives overlaps the first cache tile.